RAID with mixed disk technology

You meaning using both SSD's and spinning disks in the same array? :scratch:

Basically in pretty much all RAID arrays you get the performance of the slowest drive by the number of drives. So, for example if you made a RAID-5 array out of 2 500GB 7200RPM drives, 1 500GB 10,000RPM drive, and 2 500GB 5400 RPM drives, you would get the performance of a 5 x 500GB 5400 RPM drive array. So, your SSDs would be neutered by the spinning discs they share the array with.

I suppose if you tried a RAID-0 or RAID-1 of a JBOD SSD / spinning disk array it would work, but ultimately I don't know why you might bother.

if you took a pair of 80GB SSDs and a pair of 1TB 5400 RPM drives you could make two JBOD arrays (80GB + 1TB) and then RAID-1 or AID-0 those two arrays and end up with a single volume that had very high performance for the first 80GB (RAID-1) or 160GB (AID-0) and reduced for the rest. Buy why? :bstd:
 
You could try it in a Drobo. They do some weird things with matching disparate drives. I don't understand the purpose.
 
I mean striping mirrors of mixed technology.

In a mirrored configuration the controller will ask for data alternately from either drive because it is assumed that they are close in performance. You could weight one drive more heavily than another but IFAIK no mass market raid controller will do that. Maybe Linux softraid will do it.

When reading a mirror the controller will ask the first one available. If the ssd can be designated as always most available then Bobs your uncle. Writes are typically limited to the speed of the slowest disk. This could possibly be mitigated by dedicating the Raid cache to the spinning disk and increasing the cache so that a majority of writes are not random. Not to meantion it wouldn't be contending with read seeks.
 
It sounds like you're really talking about creating an online real time synchronized "backup", not a RAID-1 array. I don't have much experience with these. My opinion is you'd rather have a scheduled backup than a real-time one.

If we hypothetically assume the "backup" is instant or real-time it's worthless because any damage done to the data on the primary drive is immediately done to the "backup". RAID-1 (like all RAID levels, 0 excluded because it's not RAID) is insurance against downtime not data loss or corruption. In such a case having a spinning disc as the fall back when the primary failed would mean reduced performance which may or may not be acceptable.
 
I'm interested in a different combination: an SSD shadowed by an HDD.

Shadowed because:

* RAID would lose the benefits of the SSD
* HDDs are typically far, far larger than SSDs

My reasoning is that SSD reliability is likely to be far superior to HDD - once it's a more mature technology anyway. So for modest systems, I don't think realtime redundancy will be mandatory. There's not much point in duplicating something that may turn out to be almost as reliable as a RAID controller, for instance. But you still need online backup, so ...
 
time said:
Seagate Momentus XT have just 4GB of flash, and that's used as a read-cache (not write).

I'm talking about full performance on SSD, with periodic backup to HDD.
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I've been able to get close with TrueImage. You can establish backups on a two hour threshold if you want. New versions of TrueImage have support for nonstop backup, but I haven't tried it out. Carbonite also does backup in real time.
 
Probably not automatically, though you might be able to script it. I was just thinking about what I would need to talk the user through on the phone to get them back up and running.
 
No, not automatically. TrueImage can't do scripted restores, either. It's not a difficult process to restore, but it is a bit obnoxious because the Rescue/Boot Time environment has a different interface from the Windows program.
 
How about CMS BounceBack?

* Boots from backup device when primary storage fails
* Then presents two choices: Continue or Restore
* Continue runs the system directly from the backup device
* Restore copies the image to replacement primary storage
 
Mercutio said:
No, not automatically. TrueImage can't do scripted restores, either. It's not a difficult process to restore, but it is a bit obnoxious because the Rescue/Boot Time environment has a different interface from the Windows program.
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Linux vs. the Windows?
 
I think it's more that they didn't take the time to update the interface on the rescue side. There's no technical reason why one version can't look like the other.
 
ddrueding said:
Interesting. Their Server Product is also very interesting. Massively reasonable considering the competition.
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Possibly not as much as you think. Acronis SBS edition and Backup Exec are both around that price and have the distinct advantage of being much more familiar products. A Google Products search shows TrueImage Server 10 for $450, too.
 
List Prices

CMS BounceBack SBS Software (boxed) $295
Acronis Backup & Recovery 10 Advanced Server SBS Edition $499
Backup Exec System Recovery Server Edition "from $891"
Backup Exec for Windows Small Business Server "$1003-$1045"

What are you smoking?
 
None of those run MS SQL Server.

Also, it's a hell of a lot easier to find someone to help out with a Windows server than any of the 'nixes.
 
time said:
None of those run MS SQL Server.

Also, it's a hell of a lot easier to find someone to help out with a Windows server than any of the 'nixes.
Click to expand...

The other side to that is that I have customers using LAMP stuff that was set up years ago and I've never touched it since. At this point I'd have to review my notes on how it's set up because I don't even remember.

I have customers doing stuff on Windows machines where I have to do SOMETHING to their servers once a week. Right now I'm dealing with a machine that hangs on shutdown. No log entries, no hard failures. It just doesn't finish shutting down.

So at some point I'm going to have to go screw around with system services and watch it start up and reboot twenty or thirty times to figure out what the hell is going on.
 
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